Pulsars in close binary orbit around another neutron star or a massive white dwarf make ideal laboratories for testing the predictions of gravitational radiation and self-gravitational effects .
We report new timing measurements of the pulsar–white-dwarf binary PSR J1141 - 6545 , providing strong evidence that such asymmetric systems have gravitational wave losses that are consistent with general relativity .
The orbit is found to be decaying at a rate of 1.04 \pm 0.06 times the general relativistic prediction and the Shapiro delay is consistent with the orbital inclination angle derived from scintillation measurements .
The system provides a unique test-bed for tensor-scalar theories of gravity ; our current measurements place stringent constraints in the theory space , with a limit of \mbox { $ { \alpha _ { 0 } ^ { 2 } } $ } < 2.1 \times 10 ^ { -5 } for weakly non-linear coupling and an asymptotic limit of \mbox { $ { \alpha _ { 0 } ^ { 2 } } $ } < 3.4 \times 10 ^ { -6 } for strongly non-linear coupling , where { \alpha _ { 0 } } is the linear coupling strength of matter to an underlying scalar field .
This asymptotic limit is nearly three times smaller than the Cassini bound ( \mbox { $ { \alpha _ { 0 } ^ { 2 } } $ } \approx 10 ^ { -5 } ) .